Unless you installed your operating system from floppies, chances are that you have a bunch of programs running on your computer at any one time. There are enough things that can go wrong in any one particular program and when you add them into the same soup, the interactions between them create more scenarios where things can go awry. The operating system has ways of preventing programs from mucking with each other via protected memory and resource limits but it’s not that surprising when some program will interfere with another.
It’s something I have to deal with a lot with Hazel. Since Hazel runs in the background and manipulates files it does not have full control over, there’s a lot to be watch out for. I have to coordinate with browsers to make sure not to move the file while it’s still being downloaded. I try and detect when the user is copying something with the Finder (which for some reason uses ‘brok’ as the file type instead of the ‘bzy ‘ or ‘bzy?’ types which I believe was the convention from the older MacOS days). I run my background processes with lower priority and even use low priority IO. Try this test. Take a large file and copy it. Turn off Hazel’s trash management options, move one of the files to the trash and use Finder’s “Secure Empty Trash”. Observe how usable your machine is while this is happening (for me, the answer is “barely”). Now, turn on Hazel’s trash management, setting the trash size threshold to something lower than the file size. Set Hazel to throw away oversized files immediately and to do so securely. Now, throw away the other file. You can tell something is happening but at least from all my tests, my machine is more responsive.
So, it’s a bit frustrating when you go through the trouble of making your software a good citizen when someone else’s software goes out of their way to interfere with yours.
A while back, I got a report from a customer that Hazel was not working. Looking at the logs, the customer noticed that it would stop working whenever he ran Logic Pro. When he quit Logic, Hazel would magically work again. At first, I didn’t believe it. It seemed too weird but I downloaded a trial of Logic Express and sure enough, I experienced the exact same behavior. After a bit of poking around I discovered what was happening. Logic Pro/Express stops all launchd jobs. Hazel uses launchd to start its background processes so it was a bit disconcerting to see another program, especially one from Apple, disabling yours on purpose, albeit indirectly. At least Logic is nice enough to start the jobs again when it quits.
Now, I’m sure the Logic team is probably doing this to ensure a level of performance but scouring the Apple lists and the web at large turned up nothing about this behavior. Maybe a tech note somewhere would have been nice. It’s unclear if any of Apple’s other pro apps exhibit this behavior but at least now I know what to look for.
Should this be a preference in Logic? Maybe a warning when it detects that the user has their own launchd jobs? I know it’s not common for software out there to depend on launchd but it is pretty annoying for those of us it does affect. I could write my own daemon using kqueue (which launchd uses to monitor file changes). Logic will not interfere with it then, but part of me feels that this would make Hazel impolite. Logic is doing what it’s doing for a reason and to work around its intentions goes against Hazel’s good manners. So for the time being, I’ll just have to accept that the housekeeper must go on break whenever the cops come in to commandeer the house.